1. Field of the Invention
The present invention generally relates to an image processing apparatus, an image reading apparatus, an image forming apparatus and a recording medium for storing an image processing program.
2. Description of the Related Art
Recent developments of techniques associated with input and output of images have strongly stimulated a demand for higher-definition images. For example, digital still cameras, which are a kind of image input apparatuses, are in widespread use at present because of rapid price reduction of high-performance charge coupled devices (CCD), which play an integral part in the digital still cameras, that have the number of effective pixels greater than three millions. On the other hand, image output apparatuses and image display apparatuses, such as laser printers and inkjet printers, are also experiencing remarkable quality increases and drastic price decreases. In addition, such phenomena can be also observed in the field of image forming apparatuses such as copier and multifunction products (MFP).
As such higher-performance and more affordable image input and output products are offered in markets, high-definition images would become available to a greater number of peoples. In the future, it is estimated that such popularity can boost a demand for high-definition images everywhere.
Across the stream, it is predicted that there arises a growing demand for useful image compression and decompression techniques that make it possible for users to deal with high-definition images without difficulty. In an existing JPEG 2000 standard, which is one of conventional image compression and decompression schemes for high-definition images, an original image is partitioned into components and is processed per component, as appreciated by those skilled in the art. According to the JPEG 2000 standard, it is possible to decode and reconstruct a high quality image from its underlying compressed image even if the underlying image is compressed at a high compression rate.
There is an increasing tendency to equip an image forming apparatus, such as a copier and a multifunction product, with compression and decompression techniques such as the JPEG 2000 standard for the purpose of less memory consumption. Such an image forming apparatus compresses an original image, which is read by an image reading device installed in the image forming apparatus, and stores the coded image data in a working memory for the moment. Then, when the image is about to be printed out, the image forming apparatus decompresses the coded image data in accordance with the reverse compression procedure, that is, the decompression procedure, and supplies the decoded image data to a printer part thereof to output the underlying image.
In addition, some of copiers and multifunction products of today have various useful functions. Among such functions, there is an image synthesis function to synthesize two images.
FIG. 1 shows an example for explaining a conventional image synthesis process. As shown in FIG. 1, for example, such an image forming apparatus having an image synthesis function can superpose a pattern image Y, such as “URGENT”, “CONFIDENTIAL” and a company logo, onto a desired position of an original image X, and output the synthesized image. Throughout this specification, the term “image synthesis” is not limited to syntheses of given original images, such as superposition of an overlapping portion the original images each other or reverse of a superposed portion of the original images. The image synthesis according to the specification includes various types of syntheses, for example, superposition of a pattern image, which is stored in a memory in advance, onto a given original image. For example, a ruled line image is provided as such a pattern image to an image forming apparatus in advance. In this case, when receiving a given document, the image forming apparatus can produce a synthesized form document such that the original document is adequately superposed on the ruled lines.
Conventionally, in order to synthesize coded images, an image forming apparatus decodes the coded images into their underlying images and synthesizes the decoded images, for example, through bitmap expansion, as appreciated by those skilled in the art. Then, the image forming apparatus encodes the synthesized image again and produces the resulting encoded image as a result of the synthesis
However, such a synthesis process requires a large processing time, because the resulting encoded image is obtained through the decoding process, the image synthesis process, and the encoding process. In addition, when the image forming apparatus decodes a target coded image into its underlying image, it is necessary to prepare a working memory to temporarily store the decoded image data for the image forming apparatus. In particular, when the image forming apparatus decodes coded data of the whole image, the image forming apparatus has to include an additional working memory such as a page memory.